The lifespan of a toner cartridge is determined by the reset chip on the cartridge. During the printing process, the fill level stored on the chip is reduced steadily. Once the fill level has reached 0%, the chip has expired. By replacing the chip with a new one, the cartridge is recognized as new/full again by the printer. The toner/reset chip has to be replaced once the printer shows the message "toner empty / replace toner". The chip should only be replaced after the cartridge has been refilled.
We explicitly advise against replacement of the chip without refilling of the cartridge, as this only works in exceptional cases and the full print capacity of the chip is not used. Each toner chip can only been used once and is unusable afterwards, as the fill level information stored on the chip can only be reduced and not increased again.